Posts

,

API6D Ball Valve Types and Features

API 6D is a standard set by the American Petroleum Institute (API) for valves used in pipelines transporting oil, natural gas, and other liquids. API 6D defines the design, manufacturing, testing, and quality assurance requirements for various types of valves, including ball valves, used in these critical applications.

Types of API 6D Ball Valves

API 6D Ball Valves are designed to ensure reliability, performance, and safety in pipeline systems. There are several types of ball valves that conform to the API 6D standard:

  1. Floating Ball Valve
    • Design: In a floating ball valve, the ball is not fixed to the stem but is allowed to “float” within the valve body. It is pressed against the valve seat by the fluid pressure, ensuring a tight seal when the valve is closed.
    • Application: Suitable for low-pressure and medium-pressure systems, as the ball relies on the pressure of the fluid to create a seal.
  2. Trunnion Mounted Ball Valve
    • Design: A trunnion-mounted ball valve has a ball that is fixed at two points (top and bottom) by trunnions (supporting shafts), allowing the ball to remain stationary and only rotate. This type of valve typically requires less actuator torque than a floating ball valve.
    • Application: Suitable for higher pressure applications and large-diameter pipeline systems. Trunnion valves are generally preferred in applications where sealing performance and low torque are crucial.
      China Trunnion Ball Valve
  3. Top Entry Ball Valve
    • Design: The valve body allows for maintenance or servicing of the valve components (such as the ball and seats) through the top without removing the valve from the pipeline.
    • Application: Used in systems where easy maintenance is essential without system shutdown or disassembly.
  4. Side Entry Ball Valve
    • Design: In a side-entry ball valve, the valve body is designed such that the ball and stem assembly is inserted from the side.
    • Application: Typically used in smaller sizes and more accessible locations for easier maintenance and installation.
  5. Full Port (or Full Bore) Ball Valve
    • Design: A full port ball valve has a bore (internal diameter) that matches the pipe’s internal diameter, offering minimal flow resistance and full flow capacity.
    • Application: Ideal for applications requiring unrestricted flow, like pipelines carrying sensitive materials or substances that need to maintain flow integrity.
  6. Reduced Port (or Reduced Bore) Ball Valve
    • Design: In a reduced port ball valve, the bore is smaller than the pipe diameter. This results in some flow restriction compared to a full port ball valve.
    • Application: Typically used where space is constrained, or flow capacity is less critical.

Key Features of API 6D Ball Valves

  1. Design Pressure and Temperature Range:
    • API 6D ball valves are designed to withstand a wide range of pressures and temperatures based on the valve class. The design ratings ensure that they perform safely and effectively in both standard and extreme conditions.
  2. Material Selection:
    • The materials used in API 6D ball valves are chosen for their resistance to corrosion, erosion, and wear, as well as their ability to handle high pressures and temperatures. Common materials include stainless steel, carbon steel, and various alloys like Inconel and Hastelloy.
  3. Fire-Safe Design:
    • Fire-safe ball valves are designed to continue to operate in the event of a fire. These valves are typically equipped with secondary sealing mechanisms (e.g., graphite or metal seals) that provide sealing integrity even under high heat conditions.
  4. Blowout-Proof Stem:
    • A blowout-proof stem is a critical feature for safety. It ensures that the valve stem cannot be dislodged, even under extreme pressure, preventing accidental release of valve contents.
  5. Anti-Static Features:
    • Some API 6D ball valves are designed with anti-static features that prevent the accumulation of static electricity, reducing the risk of sparks in volatile environments.
  6. Seat Materials:
    • The valve seats are typically made from soft materials like PTFE, PEEK, or elastomers, but can also be made from metal for higher temperature or more abrasive applications. Seat designs can vary depending on the application, with options for sealing at high pressures, low pressures, or extreme temperatures.
  7. End Connections:
    • API 6D ball valves typically come with various end connections, including flanged, threaded, and welded types. Flanged ends are most common, as they allow easy installation and removal from the pipeline.
  8. Actuation Options:
    • API 6D ball valves can be manually operated (via handwheel or lever) or automatically operated (via electric, pneumatic, or hydraulic actuators). Automated actuation is often used for remote operation or in hazardous environments.
  9. Double Block and Bleed (DBB) Feature:
    • Some API 6D ball valves offer a Double Block and Bleed feature, which ensures a tight seal on both sides of the valve and allows for the safe venting of any trapped fluids between the seats. This is essential for ensuring safe maintenance and operation.

API 6D Ball Valve Applications

  • Oil & Gas Pipelines: Used extensively in the transport of crude oil, natural gas, and refined products.
  • Chemical Processing: Valves are used for the controlled flow of chemicals and other reactive fluids.
  • Water Treatment: Used to control the flow of water in treatment plants.
  • Power Generation: In power plants, ball valves regulate steam, water, and fuel in various stages of the generation process.

Summary of API 6D Ball Valve Types and Features

Type of Valve Design Features Application Areas
Floating Ball Valve Ball “floats” to create a seal, relies on fluid pressure Low to medium pressure systems
Trunnion Mounted Ball Valve Ball fixed with trunnions, lower torque required High pressure and large-diameter pipelines
Top Entry Ball Valve Servicing from the top without removing valve from pipeline Applications requiring easy maintenance
Side Entry Ball Valve Ball assembly inserted from the side Smaller systems or accessible locations
Full Port Ball Valve Full bore matching pipe diameter Unrestricted flow, sensitive materials
Reduced Port Ball Valve Bore smaller than pipe diameter Space-constrained applications

Conclusion

API 6D ball valves are designed to provide reliable, durable, and safe service in pipeline systems, especially in the oil and gas, chemical, and power generation industries. The wide variety of designs and features available ensures that these valves can meet specific operational requirements, whether dealing with high pressure, extreme temperatures, or corrosive materials

/by
,

The floating ball valve vs the trunnion mounted ball valve

‘’Floating ball’’ and ‘’trunnion ball’’ are concepts which are used generally. But what are the exact difference between these two designs and when to use which one?

The most important difference between these two design is the construction of the ball and the way in which it is assembled inside the valve body. A trunnion ball is attached and centred inside the valve body through both a top shaft -the valve stem- and a bottom shaft – the trunnion. A floating ball is attached to the valve body only through the valve stem. As a result, the floating ball ‘’floats’’ in the valve seats.

In a floating ball design the ball is pushed against the downstream seat by the in-line pressure, resulting in tightness. When operated from closed to open position, the ball is to be rotated against both the in-line pressure (∆p) and the friction of the seats. In other words: the torque needed to operate the valve is created by both in-line pressure and the nature of the valve seats. The amount of torque required increases significantly when operating pressure (∆p) and/or valve size increase, and/or whenever the nature of the seat is made more robust. The latter applies in case of a metal seated valve design.

Floating ball
Trunnion ball

In a trunnion design, the ball is inserted in a central bottom shaft which is called the trunnion. The ball is fixed between the stem and the trunnion, which inclines that the ball is not floating but fixed and centred. The inline pressure presses the seats against the ball, causing the tightness. This inclines that during operation, the ball does not have to be rotated against the in-line pressure (∆p) and the valve seats, but that is solely needs to be rotated against the pressure of the seats.

 

Floating ball & trunnion ball

As a result, the required torque of a trunnion mounted ball valve is generally lower than the torque required of a comparable floating ball valve. For example: a DN200 metal-seated floating ball valve would require a significantly larger actuator than a DN200 comparable trunnion valve, leading to significantly lower costs of the overall package. Also, in general the trunnion seat design offers higher stability which makes it more suitable for extreme conditions and especially varying pressure levels.

So, the trunnion-mounted ball valve is more suitable for high pressure applications and bigger dimensions compared to the floating ball. Another advantage of the trunnion design vis-à-vis the floating design is the fact that a trunnion generally is included with a drain or bleed connection, making it suitable to function as a dual safe device. Furthermore, it functions as an relief valve automatically whenever the pressure in the central cavity is higher than the spring force of the seats. When this happens, the seat springs relieve automatically in order to drain the excess pressure back into the main line. Because of these reasons, the trunnion is commonly used in offshore- & oil & gas applications, where extreme conditions pose the standard.

Off course, a large disadvantage of the trunnion compared to the floating design is associated with its costs; which are significantly bigger. Because of these costs, trunnions are used solely when they have to be used.

Our specialist happily assist you in advising the right ball valve design for your application.

/by
,

Ball Valve Basics

Welcome to the first in a series of Valve Basics articles, each focused on a major product type and written especially for newcomers to the industries that use and make valves and related products.

Ball valves may not bounce very well but they work great at regulating flow. The popular valve is named for its round ball that sits in the interior of the valve body and pushes into a seat to control or provide on/off functions in fluid pipelines.

API 6D trunnion ball valves.

API 6D trunnion ball valves.

The heritage of ball valves is much shorter compared to gate, globe and check valve designs. Although the first ball valve patent was issued in 1871, it would take another 85 years for ball valves to become a commercial success. The discovery of polytetrafluoroethylene (PTFE, or “Teflon”) during the process design for manufacturing the atomic bomb in World War II, would be the catalyst that started the ball valve industry rolling. Ball valves come in all materials from brass to carbon steel and stainless steel to zirconium.

There are two basic types: floating ball and trunnion ball. These two designs allow for the construction of effective ball valves from ¼” through 60” and larger. Generally, the floating design is used for smaller and lower-pressure valves, while the trunnion type is used for larger and higher-pressure valve applications.

Floating ball valve.

Floating ball valve.

The reason for the two types of ball valves has to do with the way they seal and how the fluid force is distributed from the line flow to the ball and then to the seat. In the floating ball design, the ball is riding snugly between two seats, one upstream and one downstream. The force of the fluid acts on the ball to push it into the seat located in the downstream valve body. Since the ball covers the entire flow bore, all the force in the stream is pushing against the ball to force it into the seat. If the ball gets to be too large and the pressure too high, the force will be so great on the seat that the valve cannot be operated because the operating torque would be too high.

Floating ball valves come in a variety of body styles, although the two-piece, end entry type is the most popular. Other body styles include three-piece and top entry. Floating ball valves are manufactured in sizes up to 24” and class 300, but the practical realm of the floating ball valve is generally much lower—up to about 12”.

Although ball valves are designed primarily to be on/off or “block” valves, the addition of partial ball and V-port ball designs can make them good choices for control-type applications.

RESILIENT SEATS

The smaller floating ball valves are found in many different applications from household plumbing to those containing the harshest chemicals. The most popular seating material in these valves is some form of thermoplastic, such as PTFE. PTFE seats work very well because they are soft enough to seal well on to the polished metallic ball, yet firm enough not to blow out of the valve. The two primary concerns with these soft-seated valves are that they are susceptible to scratching (and potential leakage) and are limited to temperatures below the melting point of the thermoplastic seats—somewhere around 450oF (232oC) depending on the exact seat material.

A ball valve

A ball valve “ball.”

A feature of many resilient-seated floating ball valves is the ability to moderately seal in the event of a fire that causes the primary seats to melt. This is called a fire-safe design; it features a seat pocket that not only holds the resilient seat in place, but also provides a metallic seating surface that can provide a partial seal as it contacts the ball. The fire-safe design is confirmed by testing the valve in accordance with the American Petroleum Institute (API) 607 or 6FA fire-testing standards.

TRUNNION DESIGN

When larger sizes and higher-pressure ball valves are needed, the design shifts to the trunnion style. The trunnion differs from the floating style in that the trunnion ball is held in the body via a trunnion (short, attached stem) in the bottom and by the stem at the top. Since the ball cannot “float” into the seat to attain positive closure, the seat must float to the ball instead. The trunnion seat is designed so that the seat is energized by the upstream pressure and is forced into the ball to seal. Because the ball is held securely in place, except for its 90o rotation, the extraordinary fluid force and pressure does not jam the ball into the seat. Instead, the force acts only on a small area on the periphery of the floating seat.

The trunnion ball valve is the brawny big brother to the floating ball valve and as such it gets to handle the big jobs—high pressures and large pipe diameters. By far the most popular use of trunnion ball valves is for pipeline service. These valves are especially popular in natural gas pipelines in diameters up to 60” and pressures up to class 600. Trunnion ball valves can also be used in higher pressures if required. By using trunnion designs the torque required to open and close the valve is lower, so smaller actuators can be used.

End-entry design.

End-entry design.

The trunnion design also lends itself well to double block and bleed service since both the upstream and downstream seats float independently and most designs also feature a body or drain connection. Trunnion designs often employ seat lubrication ports where a lubricant can be injected around the seat to assist in closure efficacy.

METAL-SEATED DESIGNS

The biggest advancement in ball valve technology over the past 30 years or so is the metal-seated ball valve. While the idea of metal seats and a metal ball are not new—in fact, the first ball patent in 1871 featured a brass ball and brass seats—the design needed advancements in coating technology to really be perfected.

The metal-seated ball valve design has enabled ball valves to take a big chunk out of the market share dominated for decades by the venerable gate valve. The metal-seated, specialty-coated ball closes tightly against a set of precision coated and lapped seats, providing zero-leakage, if the hardened seating surfaces are not scratched by debris in the line.

BALL VALVE STANDARDS

The are several standards that apply to ball valves. The following table lists the most common ball valve design documents:

Ball valves have made huge inroads in replacing other valve types over the past 40 years. The cost to manufacture the smaller sizes has dropped greatly as well, making them even more competitive. The advances in coatings and metal-seated ball valve technology have created very robust designs that have resulted in an attractive total cost of ownership.

Table 1. Common ball valve standards.

Table 1. Common ball valve standards.

While the overall industrial valve segment is still dominated by gate and globe, linear-valve designs, the relatively young ball valve is steadily making up ground, and the metal-seated types have become the preferred valve design for severe-service applications around the world.

In need of assistance in selecting a ball valve ? The experts at STV VAlVE have the knowledge and experience to help. Shop stvvalve.com today!
/by